Update airflowHost in webhook translator to point to osm-webserver

This is a workaround put in place while Airflow helm chart is not
dealing properly with the value `fullnameOverride`, which is required
now that Airflow is a subchart of OSM Helm chart.

The issue in Airflow is reported in this link:
https://github.com/apache/airflow/issues/22622



Change-Id: I8e8a068a1386121c2d2196fdaed550fbd693d9d5
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>